Surface Water and Ocean Topography Mission (SWOT)Lee-Lueng Fu (Jet Propulsion Laboratory)

A snapshot of sea surface height anomalies from T/P and ERS altimeters

22 )0()( CdssCL

Correlation of SSH time series as function of spatial separation

A spatial scale computed as follows:

km

L= 210 km

SSH wavenumber spectra (Ducet et al. 2000)

T/P along-track

T/P-ERS mapped

T/P mapped

Overlapping at 150 km

Spatial scales of the AVISO T/P-ERS merged data

Scales shorter than 150-200 km are not resolved.

210 km

Small-scale Variability of the Ocean Unresolved by Nadir-looking Altimeter

100 km

ground tracks of Jason (thick) and T/P (thin) Tandem Mission

100 km scale eddies resolvable by WSOA

10 km scale eddiesResolvable by HM

41.9º N

42.5º N

< 10 km

< 10 km

Coastal currents have scales less than 10 km

< 10 km

Observations made by ADCP offshore from the US

West CoastT. Strub

h ~ 5 cm v ~ 50 cm/sec

SWOT Measurement ConceptA SAR interferometry radar altimeter Near-global coverage with

16-day repeat orbit

• Same technique as WSOA – radar interferometry• Use of SAR to enhance the along-track resolution• 2 cm measurement precision at 2 km resolution• 1 micro-radian precision in mean sea surface slope at 2 km resolution • No data gap near the coast

87654321 N

umbe

r of

Obs

erva

tion

SWOT Orbit Sampling

Obs

erva

tions

/cyc

le

Altimetry SSH wavenumber spectrum

Wavenumber (cycles/km)

Pow

er d

ensi

ty (c

m2 /c

ycle

s/km

)

Noise level of HM for 2 cm measurement noise at 2 km resolution

Jason pass 132 (147 cycle average)

Stammer (1997)

T/P

T/P

?

?

Much reduced noise floor will enable the study of the spectrum at sub-mesoscales which have not been well resolved from existing data.

= 1cm/km(or 0.4 cm/7km)

= 2cm/2km (or 1 cm/7km)

= 2cm/7km

For the three cases, velocity error is reduced from 7.8 to 3.6, 1.3 cm/sec at 25 km resolution;

or 27, 15, 5 cm/sec at 10 km resolution

Wavenumber (cyc/km)

Vel

ocity

err

or (c

m/s

)2/ cy

c/km

Geostrophic velocity error spectrum100 50 25 km

McWilliams (2006)

Sub-mesoscale variability

Sub-mesoscale processes are poorly observed but important to the understanding of the dissipation mechanism of ocean circulation.

Radius of deformation

Radius of deformation

Hydrology applications• Our knowledge of the spatial and

temporal distribution of surface waters is poor– Unconfined hydraulics of wetlands– Lakes and reservoirs are globally

distributed but not measured– Under-developed economic and political

infrastructures• Hydrologic Science and Applications

Issues:– Need to constrain water and energy cycle

models with surface water discharge and storage changes, globally & consistently

– Improve understanding of flow hydraulics, especially for flood hazards

– Trans-boundary water flows are poorly known but critical for water resource management

SWOT is recommended by the Decadal Survey as a combined mission for oceanography and hydrology. A Science Working Group has been formed with additional ~200 participants from ~30 countries, and growing!

SWOT is based on the technology of SRTM and WSOA.

High-resolution ocean surface topography workshop

WATER Mission was developed for hydrology

Errors in coastal tide models up to 20 cm are revealed from the Jason-T/P Tandem Mission.

Andersen and Egbert (2005)

What is the state of the art in coastal tide modeling?

R. Ray/GSFC

Besides the intrinsic science of internal tides, they introduce 2-5 cm/sec error in ocean current velocity. Is predicting internal tides from models feasible ?

Wet Tropospheric Corrections• Land contamination in microwave radiometer observations

• OSTM has the potential for pushing the limit of coastal distance to 10 km in favorable conditions

• What are the energy containing scales of water vapor in coastal zones?

• How good is model analysis of water vapor in coastal zones?

• What new technologies are feasible for making high-resolution water vapor measurements?

• Using SAR interferometry, SWOT has the capability of mapping ocean topography at 1 km resolution next to the coast.

• Coastal tides: need models with much improved accuracies.

• Internal tides: sources of mixing in the ocean which is linked to the overall meridional overturning circulation. Also sources of errors for estimating ocean current velocity if not corrected. Need developing predictive models.

• Wet tropospheric corrections: Need to assess (1) the performance of mesoscale meteorological analysis in coastal zones, (2) new technologies for making high-resolution water vapor measurements.

Conclusions